A team of NASA and Stanford scientists will discuss its findings showing strong circumstantial evidence of possible early Martian life,
including microfossil remains found in a Martian meteorite,
at a news conference scheduled for 1:00 p.m. EDT, August 7, at NASA Headquarters, 300 E. St. SW, Washington, DC.
The team's findings will be published in the August 16 issue of Science magazine.

The briefing will be carried live on NASA TV
with two-way question-and-answer capability for reporters covering the event from participating NASA centers.
Audio of the broadcast will be available on voice circuit at the Kennedy Space Center by calling 407/867-1260.

NASA Television is broadcast on Spacenet 2, transponder 5, channel 9, C-Band, located at 69 degrees West longitude,
with horizontal polarization. Frequency will be on 3880.0 megahertz, with audio on 6.8 megahertz.

"NASA has made a startling discovery that points to the possibility
that a primitive form of microscopic life may have existed on Mars more than three billion years ago.
The research is based on a sophisticated examination of an ancient Martian meteorite that landed on Earth some 13,000 years ago.

The evidence is exciting, even compelling, but not conclusive.
It is a discovery that demands further scientific investigation.
NASA is ready to assist the process of rigorous scientific investigation and lively scientific debate that will follow this discovery.

I want everyone to understand that we are not talking about 'little green men'.
These are extremely small, single-cell structures that somewhat resemble bacteria on Earth.
There is no evidence or suggestion that any higher life form ever existed on Mars.

The NASA scientists and researchers who made this discovery will be available at a news conference tomorrow to discuss their findings.
They will outline the step-by-step "detective story" that explains how the meteorite arrived here from Mars,
and how they set about looking for evidence of long-ago life in this ancient rock.
They will also release some fascinating images documenting their research.

- end -

American Association for the Advancement of Science News Release

Signs of Past Life on Mars?
Organic Compounds and Possible Biological Features
Found in Martian Meteorite.
Featured in 16 August 1996 Science

Washington, DC - Ever since scientists learned that water once flowed on Mars,
they've wondered whether life might also have flourished on the apparently now-dead planet.
In the 16 August issue of Science, McKay et al report the first identification of organic compounds in a Martian meteorite.
The authors further suggest that these compounds,
in conjunction with a number of other mineralogical features observed in the rock, may be evidence of ancient Martian microorganisms.

Organic (complex, carbon-based) molecules are the requisite building blocks of life on Earth.
The authors looked for signs of such molecules and other mineralogical and textural indications of past life
within the pore space and fractures of meteorite Allan Hills 84001 (ALH84001),
one of only 12 meteorites identified as having come from Mars.
ALH84001 is the oldest of the Martian dozen,
having crystallized from molten rock about 4.5 billion years ago, early in the planet's evolution,
and it is the only Martian meteorite to contain significant carbonate minerals.
(The carbonates formed sometime after the rock, perhaps about 3.6 billion years ago.)

About 15 million years ago, a major asteroid impact on Mars threw ALH84001 into space,
where it eventually fell onto an ice field in Antarctica about 13,000 years ago.
ALH84001, which shows little evidence of Terrestrial weathering,
was discovered by meteorite-hunting scientists in 1984 and only recently identified at Martian.

ALH84001 is riven with tiny fractures resulting primarily from impacts that occurred while the rock was on Mars.
The secondary carbonates formed along with some of these fractures.
The *Science* authors prepared thin sample sections that included these pre-existing fractures,
and found on their surfaces a clear and distinct distribution of polycyclic aromatic hydrocarbons (PAHs),
organic molecules containing multiple connected rings of carbon atoms
-- the first organic molecules ever seen in a Martian rock.
A variety of contamination checks and control experiments indicated that the organic material was indigenous to the rock
and was not the result of Terrestrial contamination.
For example, the authors noted that the concentration of PAHs increases inward,
whereas Terrestrial contamination likely would have resulted in more PAHs on the exterior of the rock.

The big question is: where did the PAHs come from?

It is thought that PAHs can form one of two ways: non-biologically, during early star formation;
or biologically, through the activity of bacteria or other living organisms, or their degradation (fossilization).
On Earth, PAHs are abundant as fossil molecules in ancient sedimentary rocks, coal and petroleum,
the result of chemical changes that occurred to the remains of dead marine plankton and early plant life.
They also occur during partial combustion, such as when a candle burns or food is grilled.

To address the origin of these PAHs,
the authors examined the chemistry, mineralogy, and texture of carbonates associated with PAHs in the Martian meteorite.
Under the transmission electron microscope, the carbonate globules were seen to contain fine-grained magnetite and iron-sulfide particles.
From these and other analyses, the authors developed a list of observations about the carbonates and PAHs that,
taken individually, could be explained by non-biological means.
However, as they write in their *Science* article, "when considered collectively
... we conclude that [these phenomena] are evidence for primitive life on early Mars." Some of their observations are as follows:

* The higher concentrations of PAHs were found associated with the carbonates.

* The carbonates formed within the rock fissures, about 3.6 billion years ago, and are younger than the rock itself.

* The magnetite and iron-sulfide particles inside the carbonate globules are chemically,
structurally and morphologically similar to magnetosome particles produced by bacteria on Earth.

* High-resolution scanning electron microscopy revealed on the surface of the carbonates
small (100 nanometers) ovoids and elongated features.
Similar textures have been found on the surface of calcite concretions grown from Pleistocene groundwater in southern Italy,
which have been interpreted as representing nanobacteria.

* Some earlier reports had suggested that the temperature at which the ALH84001 carbonates formed was as high as 700° C
-- much too hot for any kind of life.
However, the isotopic composition of the carbonates, and the new data on the magnetite and iron-sulfide particles,
imply a temperature range of 0° to 80°C, cool enough for life.

* The magnetite -- a mineral which contains some ferric (Fe3+) iron,
perhaps indicating formation by oxidation (the addition of oxygen) -- and iron sulfide --
a mineral that can be formed by reduction (the loss of oxygen) -- were found in close proximity in the Martian meteorite.
On Earth, closely associated mineralogical features involving both oxidation and reduction are characteristic of biological activity.

Science is the official journal of the American Association for the Advancement of Science (AAAS) in Washington, DC,
the world's largest general science organization.

The full article from Science Magazine is available at
Science On-Line:
Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001
Volume 273, Number 5277, Issue of 16 August 1996, pp. 924-930

A NASA research team of scientists at the Johnson Space Center (JSC), Houston, TX, and at Stanford University, Palo Alto, CA,
has found evidence that strongly suggests primitive life may have existed on Mars more than 3.6 billion years ago.

The NASA-funded team found the first organic molecules thought to be of Martian origin;
several mineral features characteristic of biological activity; and possible microscopic fossils of primitive,
bacteria-like organisms inside of an ancient Martian rock that fell to Earth as a meteorite.
This array of indirect evidence of past life will be reported in the August 16 issue of the journal Science,
presenting the investigation to the scientific community at large for further study.

The two-year investigation was co-led by JSC planetary scientists Dr. David McKay,
Dr. Everett Gibson and Kathie Thomas-Keprta of Lockheed-Martin,
with the major collaboration of a Stanford team headed by Professor of Chemistry Dr. Richard Zare,
as well as six other NASA and university research partners.

"There is not any one finding that leads us to believe that this is evidence of past life on Mars.
Rather, it is a combination of many things that we have found," McKay said.
"They include Stanford's detection of an apparently unique pattern of organic molecules, carbon compounds that are the basis of life.
We also found several unusual mineral phases that are known products of primitive microscopic organisms on Earth.
Structures that could be microsopic fossils seem to support all of this.
The relationship of all of these things in terms of location - within a few hundred thousandths of an inch of one another
- is the most compelling evidence."

"It is very difficult to prove life existed 3.6 billion years ago on Earth, let alone on Mars," Zare said.
"The existing standard of proof, which we think we have met, includes having an accurately dated sample that contains native microfossils,
mineralogical features characteristic of life, and evidence of complex organic chemistry."

"For two years, we have applied state-of-the-art technology to perform these analyses,
and we believe we have found quite reasonable evidence of past life on Mars," Gibson added.
"We don't claim that we have conclusively proven it.
We are putting this evidence out to the scientific community for other investigators to verify, enhance,
attack -- disprove if they can -- as part of the scientific process.
Then, within a year or two, we hope to resolve the question one way or the other."

"What we have found to be the most reasonable interpretation is of such radical nature
that it will only be accepted or rejected after other groups either confirm our findings or overturn them," McKay added.

The igneous rock in the 4.2-pound, potato-sized meteorite has been age-dated to about 4.5 billion years,
the period when the planet Mars formed.
The rock is believed to have originated underneath the Martian surface
and to have been extensively fractured by impacts as meteorites bombarded the planets in the early inner solar system.
Between 3.6 billion and 4 billion years ago, a time when it is generally thought that the planet was warmer and wetter,
water is believed to have penetrated fractures in the subsurface rock, possibly forming an underground water system.

Since the water was saturated with carbon dioxide from the Martian atmosphere,
carbonate minerals were deposited in the fractures.
The team's findings indicate living organisms also may have assisted in the formation of the carbonate,
and some remains of the microscopic organisms may have become fossilized,
in a fashion similar to the formation of fossils in limestone on Earth.
Then, 16 million years ago, a huge comet or asteroid struck Mars,
ejecting a piece of the rock from its subsurface location with enough force to escape the planet.
For millions of years, the chunk of rock floated through space.
It encountered Earth's atmosphere 13,000 years ago and fell in Antarctica as a meteorite.

It is in the tiny globs of carbonate that the researchers found a number of features that can be interpreted as suggesting past life.
Stanford researchers found easily detectable amounts of organic molecules called polycyclic aromatic hydrocarbons (PAHs)
concentrated in the vicinity of the carbonate.
Researchers at JSC found mineral compounds commonly associated with microscopic organisms and the possible microscopic fossil structures.

The largest of the possible fossils are less than 1/100 the diameter of a human hair,
and most are about 1/1000 the diameter of a human hair
- small enough that it would take about a thousand laid end-to-end to span the dot at the end of this sentence.
Some are egg-shaped while others are tubular.
In appearance and size, the structures are strikingly similar to microscopic fossils of the tiniest bacteria found on Earth.

The meteorite, called ALH84001, was found in 1984 in Allan Hills ice field, Antarctica,
by an annual expedition of the National Science Foundation's Antarctic Meteorite Program.
It was preserved for study in JSC's Meteorite Processing Laboratory and its possible Martian origin was not recognized until 1993.
It is one of only 12 meteorites identified so far that match the unique Martian chemistry measured by the Viking spacecraft
that landed on Mars in 1976.
ALH84001 is by far the oldest of the 12 Martian meteorites, more than three times as old as any other.

Many of the team's findings were made possible only because of very recent technological advances
in high-resolution scanning electron microscopy and laser mass spectrometry.
Only a few years ago, many of the features that they report were undetectable.
Although past studies of this meteorite and others of Martian origin failed to detect evidence of past life,
they were generally performed using lower levels of magnification,
without the benefit of the technology used in this research.
The recent discovery of extremely small bacteria on Earth, called nanobacteria,
prompted the team to perform this work at a much finer scale than past efforts.

The nine authors of the Science report include McKay, Gibson and Thomas-Keprta of JSC;
Christopher Romanek, formerly a National Research Council post-doctoral fellow at JSC
who is now a staff scientist at the Savannah River Ecology Laboratory at the University of Georgia;
Hojatollah Vali, a National Research Council post-doctoral fellow at JSC
and a staff scientist at McGill University, Montreal, Quebec, Canada; and Zare,
graduate students Simon J. Clemett and Claude R. Maechling
and post-doctoral student Xavier Chillier of the Stanford University Department of Chemistry.

The team of researchers includes a wide variety of expertise, including microbiology, mineralogy, analytical techniques,
geochemistry and organic chemistry, and the analysis crossed all of these disciplines.
Further details on the findings presented in the Science article include:

* Researchers at Stanford University used a dual laser mass spectrometer -- the most sensitive instrument of its type in the world --
to look for the presence of the common family of organic molecules called PAHs.
When microorganisms die, the complex organic molecules that they contain frequently degrade into PAHs.
PAHs are often associated with ancient sedimentary rocks, coals and petroleum on Earth and can be common air pollutants.
Not only did the scientists find PAHs in easily detectable amounts in ALH84001,
but they found that these molecules were concentrated in the vicinity of the carbonate globules.
This finding appears consistent with the proposition that they are a result of the fossilization process.
In addition, the unique composition of the meteorite's PAHs
is consistent with what the scientists expect from the fossilization of very primitive microorganisms.
On Earth, PAHs virtually always occur in thousands of forms, but, in the meteorite,
they are dominated by only about a half-dozen different compounds.
The simplicity of this mixture, combined with the lack of light-weight PAHs like napthalene,
also differs substantially from that of PAHs previously measured in non-Martian meteorites.

* The team found unusual compounds -- iron sulfides and magnetite --
that can be produced by anaerobic bacteria and other microscopic organisms on Earth.
The compounds were found in locations directly associated with the fossil-like structures and carbonate globules in the meteorite.
Extreme conditions -- conditions very unlikely to have been encountered by the meteorite --
would have been required to produce these compounds in close proximity to one another if life were not involved.
The carbonate also contained tiny grains of magnetite
that are almost identical to magnetic fossil remnants often left by certain bacteria found on Earth.
Other minerals commonly associated with biological activity on Earth were found in the carbonate as well.

* The formation of the carbonate or fossils by living organisms while the meteorite was in the Antarctic
was deemed unlikely for several reasons.
The carbonate was age dated using a parent-daughter isotope method and found to be 3.6 billion years old,
and the organic molecules were first detected well within the ancient carbonate.
In addition, the team analyzed representative samples of other meteorites from Antarctica and found no evidence of fossil-like structures,
organic molecules or possible biologically produced compounds and minerals similar to those in the ALH84001 meteorite.
The composition and location of PAHs organic molecules found in the meteorite
also appeared to confirm that the possible evidence of life was extraterrestrial.
No PAHs were found in the meteorite's exterior crust,
but the concentration of PAHs increased in the meteorite's interior to levels higher than ever found in Antarctica.
Higher concentrations of PAHs would have likely been found on the exterior of the meteorite, decreasing toward the interior,
if the organic molecules are the result of contamination of the meteorite on Earth.

Photographs that support today's briefing at which a team of NASA and Stanford scientists will discuss their findings showing
strong circumstantial evidence of possible early Martian life,
including microfossil ramains found in a Martian meteorite, are available via the Internet.
Real time audio of today's briefing also will be available from these sites.

NASA press releases and other information are available automatically by sending an Internet electronic mail message to domo@hq.nasa.gov.
In the body of the message (not the subject line) users should type the words "subscribepress-release" (no quotes).
The system will reply with a confirmation via E-mail of each subscription.
A second automatic message will include additional information on the service.
NASA releases also are available via CompuServe using the command GO NASA.

SEDS - SpaceViews

Breaking News

How Do We Know It Came From Mars?

Last update: 1996 August 8, 07:45 GMT

A common question asked by the public after Wednesday's announcement of evidence of life on ancient Mars
based on the analysis of a Martian meteorite was simply, "How do we know the meteorite came from Mars?"

The answer comes from a Sherlock Holmes-like detective story,
where scientists eliminated all impossible sources for a class of meteorites leaving Mars, as improbable as seemed, as the source.

There are about a dozen meteorites that fall under a classification known as "SNC", pronounced "snick."
SNC is an acronym for Shergottite, Nakhlite, and Chassigny,
three similar classes of meteorites that are quite different from all other known classes of meteorites.

In the mid-1970s, studies of the nakhlite class of meteorites showed they were much younger than typical meteorites,
with an average age of only about 1.3 billion years, billions of years younger than other small meteorites.
The chemical composition of these objects was also unusual,
with abundances of rare-earth and other elements more typical of the Earth than of other meteorites.

The first proposals that the SNC meteorites were from Mars came in the late 1970s.
These proposals were formed by process of elimination:
all other parent bodies for these meteorites were rejected to their chemical composition or orbital dynamics.

New experimental techniques in the mid-1980s provided the first solid proof that the SNC meteorites came from Mars.

Scientists were able to study tiny pockets of Martian air trapped inside of these meteorites.
The ratios of isotopes of argon and xenon, two noble gases,
found in the meteorites were very similar to ratios measured by the Viking spacecraft on Mars.

More substantial proof came soon after, when researchers found an enrichment of the isotope nitrogen-15.
This enrichment was very similar to what is found in Mars's atmosphere, and is not found anywhere else in the solar system.

Although Mars was pinned down as the source of the SNC's,
the mechanism for removing the rocks from the Martian surface and bringing them to Earth was still unknown.
By the late 1980s, Ann Vickery and Jay Melosh at the University of Arizona
found that ejection by a large impact was the most likely method for removing the rocks from Mars.

Vickery and Melosh proposed that a single impact event around 200 million years ago ejected all the known SNC meteorites,
which traveled through space for millions of years before reaching the Earth.

Evidence of Life Found In Second Mars Meteorite
Written by Ron Baalke
November 1, 1996

In a press conference yesterday,
scientists in England claimed that they've found traces of organic material in a second Mars meteorite, EETA 79001.
The same team also reported that they've found organic matter in the ALH 84001 meteorite,
the same meteorite that a NASA team reported last August as having possible microfossils.
A critical finding by the British team is that EETA 79001 contains significant amounts of organic material,
up to 1,000 parts per million.
This organic material has yet to be identified.
The British team consists of Ian Wright and Colin Pillinger from Britain's The Open University,
and Monica Grady from London's Natural History Museum.

The EETA 79001 meteorite was found in Elephant Morraine in the Antarctic,
and was the first meteorite found during the 1979-1980 collecting season.
EETA 79001 is classified as a shergotite, the most common subgroup of the Mars meteorites.
EETA 79001 weights 7,900 grams (17.4 pounds), and is the second largest Mars meteorite ever found - only the Zagami meteorite is larger.
What makes the findings from the British team particularly exciting,
is that EETA 79001 is much younger than ALH 84001. EETA 79001 is only 180 million years old - very young on the solar system scale
- and was launched into space from Mars 600,000 years ago.
The young age of this meteorite suggests that life existed on Mars much longer than what was previously thought,
and that there is a possibility that life could still exist on Mars today.

A group of British scientists has raised the stakes in the "Life on Mars" debate,
with their announcement that a second Martian meteorite contains a significant amount of organic material.
Moreover, the meteorite in question -- designated EETA 79001 -- is a relatively young rock,
an 8-kg chunk of volcanic basalt that oozed onto the Martian landscape about 180 million years ago.
The meteorite was blasted off Mars about 500,000 years ago, spending most of the time since,
wandering in interplanetary space, and it was discovered in Antarctica in 1979.

Researchers Colin Pillinger, Ian Wright, and Monica Grady found that
carbonate grains in EETA 79001 contain up to one part per 1,000 of organic material.
They made the discovery by slowly heating the rock until the organic matter vaporized,
at 300-700° Celsius, then analyzing the ratio of carbon isotopes in the escaping gas.
Pillinger notes that his team first realized that meteorite was laced with organic matter seven years ago,
but back then others argued that it had become contaminated after arriving on Earth.
This time they used a portion of the stone protected by glassy minerals from outside contact.

Full details, sky maps, and news of other celestial events appear each month in SKY & TELESCOPE,
the essential magazine of astronomy.
See our Web site at http://www.skypub.com.

Update:

Martian Meteorite Bears Signs of Life from Earth, Not Mars

Scientists Report that the Martian Rock Is Contaminated with Organic Material from Earth

The case for life on Mars seems to be becoming more difficult to prove.

The meteorite that scientists thought contained microscopic fossils of Martian life
may just be contaminated with organic material from Earth.
In the 16 January 1998 issue of Science Magazine,
two teams of researchers report that the organic carbon in the Martian meteorite Allan Hills 84001 (ALH84001)
comes from Earth and not from Mars.

In two separate papers, scientists from the Scripps Institution of Oceanography at the University of California, San Diego,
and the University of Arizona in Tucson
conclude the potato-size Martian rock was contaminated by the surrounding Antarctic ice in which it was found.
These scientists are the first to publish results of tests of organic material contained in the meteorite
since research teams at NASA's Johnson Space Center and Stanford University announced their results in August 1996.

"This is bad news with respect to using these meteorites to assess whether there ever was or is life on Mars", said Jeff Bada,
a professor of marine chemistry who headed the Scripps team.
"It shows that the meteorites aren't going to give us a definitive answer".

The Finding:
Possible Martian Microfossils

To understand this continuing scientific debate, we should review the findings of scientists
at Johnson Space Center and Stanford University.
In August 1996, they reported that they had found in meteorite ALH84001 the first organic molecules thought to be Martian in origin.
Called polycyclic aromatic hydrocarbons (PAHs),
these organic molecules were found in easily detectable amounts in tiny globs of carbonate within the meteorite.
They also noted finding several mineral features characteristic of biological activity and possible microscopic fossils of primitive,
bacteria-like organisms inside the meteorite.
Their findings were published in the August 16, 1996, issue of Science.

The scientists proposed that very primitive microorganisms may have assisted in the formation of the carbonate,
and some of the microscopic organisms may have become fossilized,
in a fashion similar to the formation of fossils in limestone on Earth.

Questioning the Finding:
Amino Acids in the Martian Rock

Bada's team at the Scripps Institution of Oceanography analyzed amino acids contained within a sample from the meteorite,
while Timothy Jull's team at the University of Arizona examined the radiocarbon activity of the bulk organics.

"What we found", Bada said, "was that, yes, there are amino acids in the meteorite at very low levels,
but they are clearly Terrestrial and they look similar to amino acids we see in the surrounding Antarctic ice.
How they got in there is still an open issue".

Bada said he chose to focus his analysis on amino acids within the meteorite because, unlike PAHs,
they play an essential role in biochemistry.

An expert in the analysis of amino acids,
Bada used high-performance liquid chromatography to analyze amino acids in the meteorite to determine their "handedness".
He found that the bulk of the amino acids consisted of the left-handed forms similar to that seen in the Allan Hills ice in Antarctica
where the meteorite was found.
Bada said he could not rule out the possibility
that minute amounts of some extraterrestrial amino acids such as right-handed forms of alanine were preserved in the meteorite.

"What we and Tim Jull's team have shown is that there is no evidence in our hands that the meteorite contains any compounds
that we could definitely trace to Mars except maybe some tiny mysterious component that we don't understand at this point", he said.

Questioning the Finding:
Radiocarbon Dating the Martian Rock

A. J. Timothy Jull's group at Arizona used carbon-14 and carbon-13 tracers to determine the origin of the carbonate minerals
and organic carbon in the meteorite.
Their results indicated that the bulk of organic material in ALH84001 is contaminated material it acquired after falling to Earth.

"It looks like regular Terrestrial organic material", Jull said.
"The carbon-14 content of it suggests that there were several episodes of contamination".

Jull's team burned samples of the meteorite at different temperatures to separate organic carbon and carbonate minerals in the meteorite.
In four separate "stepped-combustion" experiments,
they collected the carbon dioxide gas produced and prepared the carbon for isotopic analysis by standard radiocarbon procedure.
At the university's Accelerator Mass Spectrometer Laboratory,
the scientists then measured how much of the heavy stable carbon isotope, carbon-13, and the radioactive carbon isotope, carbon-14,
were present in both the organic carbon and the carbonate minerals.

Jull's group is the first to report on the bulk, or main part, of the organic material in a sample of the ALH84001 meteorite.
For the past three years, Jull, a research geoscientist,
has been studying the isotopic composition of the Allan Hills meteorite to get more
information about the isotopic composition of the early Martian atmosphere.
Before Johnson Space Center and Stanford University scientists announced in August 1996 the possible existence
of bacterial fossils in the meteorite, several scientists, including Jull,
had discovered that the carbonate minerals of the meteorite were far richer in carbon-13 than are any carbonates on Earth.

"This unusual signal (carbon-13 enrichment)
tags the carbonate minerals in the Allan Hills meteorite as likely formed from a reservoir such as the Mars atmosphere", Jull said.

He and his team now also have discovered that the abundance of carbon-13 in the organic carbon in the meteorite
is an exact match to the abundance of carbon-13 in Earth's organic carbon.
"It looks like regular Terrestrial organic material, with the exception of one small component in ALH84001".
The researchers say they suspect that this component is some carbon indigenous to the rock,
possibly associated with a mineral phase, that burns at higher temperatures.

The carbon-13 data alone are convincing evidence that the organic carbon in the meteorite is
"regular Terrestrial organic material", Jull said.
"Combining this with the carbon-14 evidence is the clincher", he added.

Radioactive carbon is produced when cosmic rays from space strike Earth's atmosphere and react with nitrogen.
Carbon-14 also can be produced in minerals irradiated in space and on Mars, by high-energy nuclear reactions.
However, Jull and his co-researchers show there is no mechanism to produce carbon-14 in the organic material,
as this requires low-energy neutrons to interact with nitrogen atoms.
Thus, organic material which originated on Mars would contain a negligible amount of radioactive carbon before it fell to Earth.

Jull and his team discovered that the organic carbon in the Allan Hills meteorite contains
enough carbon-14 to yield radiocarbon ages of between 11,000 and 5,200 years.
Jull previously had determined by radiocarbon analysis of silicate minerals in the meteorite
that the rock fell to Earth about 13,000 years ago.

"The carbon-14 shows conclusively that the carbonates and the organics in the meteorite do not come from the same source", Jull said.
"It also shows the organic carbon has a Terrestrial source, likely through several episodes of contamination".

"The organic material contains 14C and the carbonate doesn't because the carbonate came from somewhere in space, presumably Mars,
and the organic material is a recent addition, which took place while the meteorite was sitting on the ice", Jull said.
"So, there is no connection between the two things".

The Question Continues

Jull said that although the scientific community can be expected to make many more discoveries about the Allan Hills meteorite,
he would be surprised if scientists got a definite answer on the question of possible ancient life on Mars from this or any other meteorite.

J. Warren Beck, an associate research scientist in physics at the University of Arizona, agreed.
"Even if we ultimately find that all the organic matter in this meteorite came from Earth,
that doesn't rule out the possibility that life may have evolved on Mars.
A meteorite represents only a tiny fragment of an entire planet", Beck said.

Bada said scientists will have to wait until a Mars mission scheduled for 2005
to bring back samples from the Martian surface to determine whether life ever graced the planet.

"In the meantime, we can throw any kind of analyses that we want to at these meteorites
and we are not going to provide an answer one way or another about whether life existed on Mars", he said.

Credits and More Information

Co-authors of the Scripps paper with Bada are Daniel Glavin, a Scripps graduate student;
Gene McDonald, of NASA's Jet Propulsion Laboratory; and Luann Becker, of the University of Hawaii.
Co-authors of the University of Arizona paper
with Jull and Beck are Christopher J. Courtney and Daniel Jeffrey of the University of Arizona.

You can find links to more information about the ALH84001 meteorite on The Planetary Society's
Hot Topics page.

Update:

SKY & TELESCOPE'S NEWS BULLETIN
MARCH 19, 1999

MORE MARTIAN MICROBES?

On Thursday, March 18th,
NASA scientists offered new evidence that fossilized microbes could be present in at least three meteorites from Mars.
Kathie L. Thomas-Keprta (NASA/Johnson) showed that the controversial stone known as Allan Hills 84001
contains many microscopic crystals of the iron-rich mineral magnetite.
One-fourth of these are perfectly shaped, same-sized hexagonal prisms free of chemical impurities.
Certain bacteria routinely produce such ultrapure magnetite crystals as a means of orienting themselves to Earth's magnetic field,
and they cannot be formed by any known inorganic process.
Of all the hints of microbial fossils seen in ALH 84001,
Thomas-Keprta says the magnetite grains provide the strongest evidence.

David S. McKay (NASA/Johnson) raised the possibility that two other Martian meteorites, Nakhla and Shergotty, contain fossilized microbes.
His scanning-electron-microscope views show a variety of round and oval forms found in tiny cracks within a Nakhla stone.
"Are they microfossils?" McKay asked aloud. "We don't know".
But he noted that the blobs are enriched in iron oxides, a common occurrence when a microbe dies and its cell becomes mineralized.
Moreover, the suspect features are a few tenths of a micron across, comparable in size to many bacteria.
(Many of the putative fossils in ALH 84001 were much smaller - too tiny, microbiologists argue, to have been viable lifeforms).
The NASA team will attempt to examine the blobs' interiors for hints of cellular structure
and to determine whether they resulted from Terrestrial contamination.
Unlike ALH 84001, which sat on the ice fields of Antarctica for 16,000 years before its discovery,
many pieces of Nakhla were recovered almost immediately after falling in Egypt on June 28, 1911.
McKay's sample came from a fragment with an intact "fusion crust" that was opened in sterile, clean-room conditions last year.

McKay also showed suspicious features from the interior of Shergotty, though the study of those is just getting under way.
Shergotty crystallized from molten rock a mere 165 million years ago,
whereas Nakhla is about 1.3 billion years old and ALH 84001 is 4 billion years old.
Thus, if microbial fossils really exist in all three of these meteorites,
it means that life has existed on Mars throughout much of the planet's history and could be there today.
NASA hopes to obtain samples of the Red Planet via spacecraft as early as 2008,
and the agency is currently wrestling with how best to isolate and study the Martian material once it reaches Earth.

Thomas-Keprta and McKay reported their results at the 30th annual Lunar and Planetary Science Conference in Houston, Texas,
which this year drew nearly 1,100 researchers - a record attendance - from around the world.

Copyright 1999 Sky Publishing Corporation.
S&T's Weekly News Bulletin and Sky at a Glance stargazing calendar are provided as a service to the astronomical community
by the editors of SKY & TELESCOPE magazine.
Widespread electronic distribution is encouraged as long as these paragraphs are included.
But the text of the bulletin and calendar may not be published in any other form without permission from Sky Publishing
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Updates of astronomical news, including active links to related Internet resources,
are available via SKY & TELESCOPE's site on the World Wide Web at
http://www.skypub.com/.

Update:

NASA Space Science News
December 20, 2000

Martian Micro-Magnets

The Allan Hills meteorite from Mars is peppered with tiny magnetic crystals that on our planet are made only by bacteria.

The case for ancient life on Mars looks better than ever after scientists
announced in December 13 '00
that they had discovered magnetic crystals inside a Martian meteorite -- crystals that,
here on Earth, are produced only by microscopic life forms.

The magnetic compound, called magnetite, Fe3O4,
is common enough on our planet. It is present, for example, in household video and audio tapes.
But only certain types of Terrestrial bacteria, which can assemble the crystals atom by atom,
produce magnetite structures that are chemically pure and free from defects.

Scientists studying the Allan Hills meteorite, a 4-billion-year-old rock from Mars that landed in Antarctica about 13,000 years ago,
found just such crystals deep inside the space rock.

Above-Right:
A transmission electron microscope (TEM) image of magnetite crystals from the meteorite.
The arrows indicate various shapes of crystals.

"Finding this type of magnetic crystal in any material from another planet is an amazing and important finding",
said Dr. Dennis Bazylinski, a geobiologist at Iowa State University.
Bazylinski leads one of the few labs capable of culturing these magnet-producing bacteria,
which are common in many freshwater and marine environments on Earth.

Bazylinski was one of nine researchers conducting the four-year investigation,
which was funded by NASA's Astrobiology Institute.
A report of their research is in the December '00 issue of the journal Geochimica et Cosmochimica Acta.

"We're not claiming that this is proof of life on Mars", said Dr. Everett Gibson,
an astrobiologist at NASA's Johnson Space Center in Houston, Texas, who also participated in the study.

"What we're claiming is that these magnetites (from the meteorite) are basically indistinguishable from certain biogenic
(i.e., biologically-produced) magnetites on Earth.
And furthermore, we know of no other mechanism to make them, either on Earth or Mars", Gibson said.

The scientists believe that these crystals traveled from Mars in the meteorite,
rather than being produced on Earth by bacteria that contaminated the meteorite after it arrived in Antarctica.

"That was a real concern - whether (the magnetite crystals) could be Terrestrial contamination", Gibson said.
But several facts support a Martian origin,
including the deep embedding of the crystals in the carbonate material of the meteorite
and the preference of the magnetite-producing bacteria for low-oxygen environments,
making it unlikely that such bacteria would live where the meteorite was found.

"We looked at it very carefully and convinced ourselves that the magnetite had to be from Mars", Gibson said.
"No one (in the scientific community) is really questioning that".

This meteorite - called the Allan Hills meteorite after the Antarctic ice sheet where it was found
- is the same one that caused a stir in 1996 by providing the first potential evidence of bacteria-like life on Mars.
These magnetite crystals were one of the four pieces of evidence from the meteorite that supported the '96 announcement.
But little was known about the specific traits of bacteria-produced magnetite then.

"At that point, we just knew that there were tiny magnetite crystals made by bacteria,
and we didn't know much about them", Gibson said. "And we now have studied (the crystals) in detail,
and ones known to be made by bacteria have the same properties (as those from the meteorite)".

Crystals made by magnetite-producing bacteria are chemically pure and free from defects in the crystalline structure.
They are slightly elongated along a particular crystalline axis,
and they range in size from 35 to 120 nanometers (a nanometer is one-billionth of a meter).
They also show a particular pattern of faceting - like a cut diamond.
These properties are so unusual that they have only been seen in magnetite crystals produced by biological processes.

The researchers discovered that about one-fourth of the magnetite crystals in the meteorite have these exact properties.
The other three-fourths of the crystals are assumed to have formed geologically, researchers said.

Magnetotactic (magnetite-producing) bacteria are able to make such precise crystals
because they control the construction of the crystal at an atomic level.

Right:
One example of a magnetotactic bacterium.
Note the line of slightly elongated magnetite crystals down the bacterium's center.
Image courtesy of Dr. Dennis Bazylinski of Iowa State University.

"The magnetites are grown atom by atom inside the bacteria.
The bacteria form a little membrane around the crystal that controls the growth of the magnetite,
and then they pump iron atoms into that membrane and form these crystals (which consist of iron and oxygen atoms).
By carefully controlling crystal growth with the membrane,
the bacteria keep the crystals from growing in one direction and allow them to grow in another", Gibson said.

The direction in which the bacteria elongate the crystals maximizes the magnetic strength of the magnetite.
The bacteria, which are mostly from the Magnetospirillum genus,
then line up several of these crystals to collectively act as a bar magnet,
which allows the bacteria to align itself with Earth's magnetic field.

Why would a bacterium want to line up with our planet's magnetic field?
It turns out that such behavior can help an aqueous microbe find water with the right mix of oxygen.
Generally, differing concentrations of oxygen in a body of water are arranged in horizontal layers, like the floors of a building.
Earth's magnetic field lines, in addition to pointing toward the pole, also make a vertical angle with the ground.
These lines provide a sort of slanted "elevator shaft" that help the bacteria search the "building's floors",
which can be more efficient than an aimless search.

But such an internal compass would be of no use to a Martian bacterium unless Mars had a natural magnetic field like Earth does.

"When we first wrote the original paper in '96, it was thought that Mars had never had much of a magnetic field", Gibson said.
"But then the Mars Global Surveyor detected a very strong remnant magnetism in some of the rocks in the crust of Mars.
... So it's clear that early on Mars had a strong magnetic field,
and that's about the time we think these magnetites were formed: about 3.9 billion years ago".

In contrast, the earliest well-documented life on Earth dates back to between 3.6 and 3.7 billion years ago, Gibson said.
Both planets formed about 4.5 billion years ago.

"Now we are trying to answer the question of whether (magnetite-producing) bacteria could have actually lived on Mars", Bazylinski said.
"And we have found certain aspects of their metabolism which suggest that they might have been able to do so".

The journal Science recently published research showing evidence of
widespread sediment layers on Mars,
which the researchers interpreted to be the product of ancient lakes that once dotted Mars's surface.
Because these lakes may have provided a habitat for bacteria,
this finding supports the possibility that the bacteria may have existed on Mars, Bazylinski said.

Though the new evidence from the Allan Hills meteorite does not prove that life once existed on Mars, Gibson said that,
"We think it's evidence that is hard to explain by any other hypothesis".

Update:

NASA News

Upper figure:
Modern magnetotactic bacteria, one showing a chain of magnetite crystals, as seen in the backscattered scanning electron microscope.

Lower figure:
Magnetite crystals and chains of magnetite crystals in the Martian meteorite ALH84001 in the backscattered scanning electron microscope.
One conspicuous chain indicated by arrows. The diameter of a single crystal ia approximately one-millionth of an inch.

"An international team of researchers has discovered compelling evidence
that the magnetite crystals in the martian meteorite ALH84001 are of biological origin."

"The researchers found that the magnetite crystals embedded in the meteorite are arranged in long chains,
which they say could have been formed only by once-living organisms.
Their results are reported in the Feb. 27 Proceedings of the National Academy of Sciences."

Update:

On 2002, David J. Barber and Edward R. D. Scott disagree with NASA on this matter:

Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001
Abstract:
Crystals of magnetite (Fe3O4) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001
were studied by using transmission electron microscopy to understand their origin
and evaluate claims that the magnetites were made by Martian microorganisms.
In magnesian carbonate, periclase occurs as aggregates of crystals (grain size ~3 nm)
that are preferentially oriented with respect to the carbonate lattice.
Larger periclase crystals ~50 nm in size are commonly associated with voids of similar size.
Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO2.
Magnetite occurs in more ferroan carbonate, and, like periclase,
it is associated with voids and microfractures and the two oxides may be intermixed.
Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate
are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates.
Magnetites in Fe-rich carbonate rims are not well oriented.
These magnetites are generally more irregular in shape and diverse in size than the euhedral variety.
All occurrences of magnetite and periclase are entirely consistent with in situ growth by solid-state diffusion
as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites.

Update:

Water in Mars

NASA Science News
March 23, 2004

More Clues Emerge to Mars' Watery Past:

Earth might not be the only planet in our solar system to have hosted salty seas.
NASA's Opportunity has uncovered evidence that the rocks near its landing site on Mars not only were once wet,
but likely formed at the bottom of a body of gently flowing saltwater.

This image shows a panoramic view of the crater
where the Opportunity rover had been exploring since its dramatic arrival in late January 2004.
The rover's lander is visible in the center of the image. Track marks reveal the rover's progress.
Image credit: NASA/JPL/Cornell.
Click for Larger Image

"We think Opportunity is now parked on what was once the shoreline of a salty sea on Mars,"
said Dr. Steve Squyres of Cornell University, Ithaca, N.Y.,
principal investigator for the science payload on Opportunity and its twin Mars Exploration Rover, Spirit.

Dr. Ed Weiler, NASA associate administrator for space science, said,
"This dramatic confirmation of surface water in Mars' history
builds on a progression of discoveries about that most Earthlike of alien planets.
This result gives us impetus to expand our ambitious program of exploring Mars
to learn whether microbes have ever lived there and ultimately whether we can."

At a press conference at NASA Headquarters announcing the findings,
NASA Administrator Sean O'Keefe said the discovery would have "profound implications for future exploration."

This magnified view from Opportunity shows a portion of a martian rock with fine layers at angles to each other.
Interpretive black lines trace layers that indicate the sediments that formed the rock were laid down in flowing water.
The interpretive blue lines point to boundaries between the layers.
Image credit: NASA/JPL/Cornell/USGS.
View Image Feature

Rippled patterns in the rocks at Meridiani Planum suggest that the land there was once a salt flat or playa,
sometimes covered by shallow water and sometimes dry, said Dr. John Grotzinger,
rover science-team member from the Massachusetts Institute of Technology, Cambridge.
Such environments on Earth, either at the edge of oceans or in desert basins,
can have currents of water that produce the type of ripples seen in the Mars rocks.

According to Grotzinger,
the sand-sized grains of sediment making up the rocks were shaped into ripples by water at least 5 centimeters (2 inches) deep
-- possibly much deeper -- and flowing at a speed in the range of 10 to 50 centimeters (4 to 20 inches) per second.

Telltale patterns called crossbedding and festooning, in which some layers within a rock lie at angles to the main layers,
led scientists to the conclusion that the rippled shapes formed under a current of water -- and not wind.
Festooned layers have smile-shaped curves that are produced when loose sediments are shifted by water.

"Ripples that formed in wind look different than ripples formed in water," Grotzinger said.
Some patterns seen in the outcrop that Opportunity has been examining might have resulted from wind,
but others are reliable evidence of water flow, he said.

So far, the findings do not specify how long liquid water covered the area, or how long ago,
but controllers at NASA's Jet Propulsion Laboratory in Pasadena, Calif.,
plan to send Opportunity out across the a plain toward a thicker exposure of rocks in the wall of a crater that should add to the story.

A second line of evidence, observations of chlorine and bromine in the rocks,
also suggests that water covered the surface when these rocks were forming.
Rover scientists presented some of that news three weeks ago as evidence that the rocks had at least soaked in mineral-rich water,
possibly underground water, after they formed.
Increased assurance of the bromine findings strengthens the case that rock-forming particles precipitated from evaporating water
as salt concentrations climbed past saturation.
See JPL News -- Minerals in Mars 'Berries' Adds to Water Story
(March 18, 2004)

Dr. James Garvin, lead scientist for Mars and lunar exploration at NASA Headquarters, Washington, said,
"Many features on the surface of Mars that orbiting spacecraft have revealed to us in the past three decades
look like signs of liquid water, but we have never before had this definitive class of evidence from the Mars rocks themselves.
We planned the Mars Exploration Rover Project to look for evidence like this,
and it is succeeding better than we had any right to hope.
Someday we must collect these rocks and bring them back to terrestrial laboratories
to read their records for clues to the biological potential of Mars."

Squyres said, "The particular type of rock Opportunity is finding, with evaporite sediments from standing water,
offers excellent capability for preserving evidence of any biochemical or biological material that may have been in the water."

NASA's Mars
Reconnaissance Orbiter, due to launch in 2005,
will survey the whole planet for sites with water-related minerals and help identify sites for future landings.

JPL engineers now expect Opportunity and Spirit to operate several months longer than the rovers' initial three-month prime missions on Mars.
To analyze hints of crossbedding, mission controllers programmed Opportunity to move its robotic arm more than 200 times in one day,
taking 152 microscope pictures of layering in a rock called "Last Chance."

Update:

An analysis of a rock sample recently collected by NASA's Curiosity rover shows ancient Mars could have supported living microbes.

"A fundamental question for this mission is whether Mars could have supported a habitable environment", said Michael Meyer,
lead scientist for NASA's Mars Exploration Program at the agency's headquarters in Washington.
"From what we know now, the answer is yes."

Last month, Curiosity drilled into a sedimentary rock near an ancient stream bed in Gale Crater.
In the powder from the drill sample, scientists have identified sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon
-- some of the key chemical ingredients for life.